Resistance temperature detectors (RTDs) are used to measure temperature by relating the electrical resistance across the RTD to the temperature. As the temperature being measured rises, so does the resistance across the RTD. RTDs are a common alternative to thermocouples for temperature measurement. While RTD's are generally more accurate than thermocouples, they are usually much slower, due to a stainless steel housing.
R. Bertram, G. Norgate and R. Isles, Thin Film Resistance Temperature Detector, U.S. Pat. No. 4,085,398 Apr. 18, 1978) discloses a resistance temperature detector which "includes a substrate of refractory dielectric material having two or more holes bored through it." A plug of electrically conductive material is fixed within each hole in proximity to one end surface of the substrate, with the plug surface preferably having a concave meniscus shape and consisting of a metal alloy such as Ni--Ti. Lead wires, such as Ni wires, are located in the holes and are connected to the plugs through the other end surface. A film of temperature dependent resistance material is deposited on the one end surface of the substrate and is connected to the two plugs. The film may consist of a thin sensing film of metal such as platinum or of a semiconductor material, deposited in a selected pattern on the substrate and in direct contact with the plugs, or the sensing film may be deposited so as to connect pads of the electrical conducting material which are deposited to cover at least a portion of the plugs. The end surface of the RTD may further have a layer of electrical insulating material to protect the sensing film.
Temperature sensors have commonly used a simple stainless steel sheath as a shield against signal noise. Current applications for specialized industries have subjected temperature sensors to widely varying RFI and EMI signals, and combinations thereof which significantly degrades this accuracy of temperatures measured by such sensors.
J. Fry, and G. Hall, Housing for a Process Controller, U.S. Pat. No. 5,010,322 (Apr. 23, 1991) discloses a combustion control system which "includes a sensor assembly and a process controller, the sensor assembly including sensors for providing output signals indicative of process variables, the process controller responding to the output signals to maintain a desired operation of the process . . . A housing enclosing the process controller provides EMI/RFI shielding of the process controller including the attenuation and absorption of the EMI/RFI energy."
While Fry et al. discloses EMI/RFI shielding for a process controller, it fails to address improved EMI/RFI shielding for temperature sensors.
In the construction and use of temperature sensors, the connection between the temperature sensor and lead wire has always created problems, both in providing a robust mechanical and electrical connection between the two, and in providing adequate shielding of the connection in some applications. Prior art junction designs have proven difficult to manufacture, and often result in breakage or frequent mandatory inspection or service.
Some prior art approaches have disclosed more robust devices, but have failed to disclose improved sensor to lead wire strain relief construction techniques. C. Kraemer, Apparatus and Method for Providing a Strain-Resistant Resistance Temperature Detector, U.S. Pat. No. 4,878,039 (Oct. 31, 1989) discloses a "strain-resistant resistance temperature element for a temperature averaging sensor and apparatus for producing same. Thin metal wire, typically of platinum, is attached to both sides of a high temperature, pliable yet stretch/strain resistant tape. A somewhat wider tape of similar description is then applied to both sides of the tape containing the sensor wire. As a result, a highly pliable, yet stretch/strain resistant temperature detector is provided".
The disclosed prior art systems and methodologies thus provide some methods for addressing response time, accuracy, and integrity of temperature sensors, but fail to provide highly accurate, fast response time RTDs with stable mounting techniques, or to provide advanced sensor RFI/EMI shielding or sensor-to-lead-wire strain relief techniques. The development of such improvements to a temperature measurement system would constitute a major technological advance.